Lithospheric stress in Mongolia, from earthquake source data

Abstract

Lithospheric stress in Mongolia has been studied using mechanisms of 84 MLH ≥ 4 earthquakes that occurred in the 20th century and instrumental seismic moments of 17,375 MLH ≥ 2.5 events recorded between 1970 and 2000. The MLH ≥ 3.5 earthquakes mostly have strike-slip mechanisms in southern and central Mongolia, with frequent reverse-slip motions in the west and normal slip in the north, especially, in the area of Lake Hovsgol. The principal stresses are, respectively, SH>Sv>Sh in the center and in the south; high horizontal compression with SH>Sh>Sv in the west; and a heterogeneous stress pattern with Sv>SH>Sh in the north. According to seismic moments of MLH = 2.5 events, oblique slip generally predominates over the territory, at Sv≈SH>>Sh, while frequent strike slip motions in the west record high horizontal compression (SH>Sv>Sh). Earthquake mechanisms show the principal horizontal compression SH to be directed W–E in the east, NE–SW in the central and Gobi-Altay regions, and approximately N–S in the west of Mongolia. The patterns of principal lithospheric stresses in the territory of Mongolia have undergone three events of dramatic change for a few recent decades, and these events were synchronous with three similar events in the Baikal rift system (BRS): in the latest 1960s, latest 1970s to earliest 1980s, and in the latest 1980s to earliest 1990s. The seismicity of Mongolia has been controlled by superposition of variable stresses associated with rifting activity pulses in the neighbor BRS on the background of quasi-stationary super-regional compression.

Keywords

• Lithospheric stress
• Mongolia
• Geodynamics
• Earthquake source data